1. Field of the Invention
The present invention relates to a method for braking a washing machine. More particularly, the present invention relates to a method for braking a washing machine by controlling a revival voltage in a motor braking system by adjusting a pulse phase and a pulse duty ratio when a revival voltage is at or below a predetermined level, and using a minimum capacity dynamic braking resistor when a revival voltage reaches over a predetermined level.
2. Description of the Related Art
Referring to FIG. 1, a conventional braking system for a washing machine comprises: a rectifier 101 which converts the AC power of the system to the DC voltage; a capacitor filter 102 which smoothes the rectified DC voltage; a motor driver 103 which drives a motor by using a smoothed DC voltage; a voltage detector 104 for detecting a voltage of the system when a motor M is suddenly braked; a voltage comparator 105 for comparing a detected voltage of the voltage detector 104 and a reference voltage pre-set in the system; a switch element 106 for determining on/off status of the dynamic brake resistor R1 according to the comparison result of the voltage comparator 105; a sensor 107 for detecting a revolution position and the speed of a motor M; a microcomputer 108 for controlling an overall operation to resolve the over-voltage in the system; and a signal output device 109 for generating a control signal according to the control of the microcomputer 108.
The dynamic braking resistor R1 converts the revival voltage into thermal energy to protect the system when the inertia energy of the motor or the load transforms into electric energy causing the level of the revival voltage charged in a capacitor filter 102 to increase.
The overall operation of the conventional braking system for a washing machine as described above is illustrated hereinafter with reference to FIG. 1.
Firstly, the rectifier 101 converts the commercial AC power supplied from the outer power source to the DC voltage, and then the DC voltage is smoothed by the capacitor filter 102 before being supplied to a motor driver 103.
The washing machine is operated as the motor driver 103 and converts the DC voltage smoothed by the capacitor filter 102 to drive the motor M.
However, in the event that a lid of the washing machine is opened during a dehydrating process or an unbalance state of the tub is detected, the rapidly rotating motor M must be braked quickly in order to make sudden stop of the tub.
Since the motor M is a brushless DC motor and it becomes the load during the normal washing operation, current flows in a discharging direction from the capacitor filter 102 to the motor M.
However, when the rapidly rotating motor M is suddenly braked, the motor M becomes a power generator and current flows in a charged direction, from the motor M to the capacitor filter 102, due to the induction electromotive power generated from the motor M causes increase in the voltage level of the capacitor filter 102.
If the revival voltage charged in the capacitor filter 102 is not discharged, then the voltage level exceeds the inner voltage of the designed circuit thereby damaging the peripheral circuit and the device.
Therefore, the voltage detector 104, the voltage comparator 105 and the dynamic braking resistor R1 are provided in order to discharge the over-flown voltage in the system during braking of the motor M.
In the event that the motor M is braked while washing or dehydration process, the voltage detector 104 measures the voltage between the capacitor filter 102 and the motor M thereof, and delivers the detected voltage measurement to the voltage comparator 105.
The voltage comparator 105 then compares the reference voltage Vref and the detected voltage Vdc delivered from the voltage detector 104, and sends the result of comparison to the switching element 106. The switching element 106 operates on/off control functions based on the compared result sent from the voltage comparator 105.
If it is determined that the detected voltage Vdc exceeds the reference voltage Vref, then the dynamic braking resistor R1 is activated as the switch is turned to on state through a power output from the voltage comparator 105.
As a result, the over-flown voltage between the capacitor filter 102 and the motor M flows to the dynamic braking resistor R1 instead of capacitor filter 102, thereby the system is sustained at the regular voltage-level as the over-flown voltage is discharged into thermal energy.
If the detected voltage Vdc between the capacitor filter 102 and the motor M is lower than the reference voltage Vref level, then the dynamic braking resistor R1 is turned off by the switching element 106 during the discharge process of the over-voltage. Then, the motor M operates as the current flows only to the capacitor filter 102, and not to the dynamic braking resistor R1.
However, when the motor M decelerates quickly or the load inertia of the motor M is massive, the revival energy generated in the motor M becomes more massive. As a result, the revival energy is revived to the motor driver 103, and the voltage charged to the capacitor filter 102 increases. And, when the DC voltage reaches over 380V, the dynamic braking resistor R1 is turned on to discharged the revival energy into thermal energy.
However, one of the disadvantages of the conventional method is that the detected voltage is compared only with one reference level, and the switching element 106 is operated to start the dynamic braking resistor R1 only in the event that the detected voltage exceeds the reference level which results in difficulty in dealing appropriately with the revival voltage according to the motor braking, and also the problem of the motor not being operated rapidly or smoothly.
Another disadvantage of the conventional method is that the size and the capacity of the dynamic braking resistor R1 installed on the outer part of the system is large making the system more complicated and increase the cost of the system.
Accordingly, it is an object present invention to provide a method for rapidly and smoothly braking a washing machine by treating a revival voltage of the motor braking with hardware and software.
Another object of this invention is to reduce the size and capacity of a dynamic braking resistor in order to reduce the system capacity and the cost.
These and other objects are satisfied by a method for braking a washing machine comprising the steps of: determining whether or not a motor is braking; transmitting a PWM (Pulse Width Modulation) control signal by setting up the initial phase and the duty ratio according to the voltage flows in the system when an operation mode determined by the previous step as a braking mode; comparing a capacity and a variance of the detected voltage with a reference voltage predetermined by the previous step; and controlling a motor driver by re-establishing the control phase and the duty ratio until the motor is stopped when the comparison result of the previous step indicates that the capacity and the variance of the voltage are lower than the predetermined reference level.